Binding liquid for molds used in precision casting



i i It; A,be,-realisetl that the 'minimumk amount of vacid 2,842,445 t 'requireclgto be gadded to the silica sol Vis that which is just.v I suicient'to make, thesol acid, but in this:case,-' the hy-f BINDING LIQUID FOR MoLDsUsEDlN w f Y PRECISION CASTING s, d rolysis reaction isinconvenientlyslow. If large amounts offacid are yadded,fa'n c l the1hydrolysisreaction carried out, vther resultinghydrolysed ethyl-silicatev solution has a: gelv timetoo shortto be ofpracticalvalue inthe investment j iROyce Lil11ifed,Delby, England, BllflSll company casting process, where A the mQuld is prepared by investing t f. u 1 an expendable patternvvith''slurry comprising apow- No Drawmgseglplltgloillary 23 195,6 10 der ed refractorymaterial:anda binding liquid. i 5 l a iThe-ethyl'silicate whichmay be used Amay for example, Claims priority, applcation Great Britain August 18,1953 be .tetrafethoxy silane (Si( OC2H5)4', or the productobj f t tained by' reacting silicon tetrachloride with 64 overY 9 Claims (Cl 106 38'35) proof ethyl alcohol as describedin British patent specifica-,J`

y v I V1.5 tion No -290 717 yThe latter roductcontains a r I rec ion investment castin rocesses a attern is Y L P PP 0X1- n p 1S g p P mately 4Q'percent1by'we1ght ofsilica and is thus prei invested in a refractory material which may be rbound by i abonding agent and then subsequentlyremoved yproduciflrghozghngylgs'a 511193 Cement 0f aPPf0 X' icenomd'm Whlch the metal lis casteo lobiam a at 20' 1 Anothenpreferred yethyl silicate is that described in fm-thesetehigfhcstsmaf sansregenerarai#aan;ninas-f* arerequire t e on ing agent or e re racto'ry, ma-

f terlal is usually prepared from an organic silicate, geny hnclidgtlltgylslftiltlanlg" 585`16%10 erally ethyl silicate, by an acid hydrolysis process.v abo' 180 P v 'i PefeeIl mili-ggEggmgga?agrsnitv n les; 25 In generalithcipreferredlethyl silicates are those whichl i meltingv dissolving in a suitable solve-nt' or by soine ri'ie-v -l1avea silica content'of at least 40% by Weight; in Carry chanica Process f i f ing out the process the ethyl silicate may be 4emulsiiied lWe have found that a mould or mould part having inl." with the silice S01 t0 which* acid has been added 1 l t l f The vstable silica solgma be re ared b ,reactin ,a creased Smngth may ljepodlld' from a refmctqry ma- 30 watersolub'le inorganic silibate gucli as sodium silicgate l, terial by using a b0I1d11 1g llqule P fePafed by cfrfymg out iur/ith an ion-exchange resin in known manner The-rethe.hydrolys1s of-.etrhyl Slha .With-a stable slhca S01 to l-'sultin solutionma be concentrated to`aslica'concenwhichy hydrochloric orsulphuric acidhas been added.V tr dog f 't le' St 3g v BYthe Premie e Stablesilic? solsfmanifa Stelle" 'aotiileomiiiis if prcaeiliii these silica son r'e'k e' A' substantiallyelectrolytmfree colloidal dispersion of silica d b 1 p -Ilow9`- y vin vvatei sometimesreferred to as a silica aquaso PreA anT mlyal Spsg'se vlhich ma be used in Carr ferred stable silica sols are those containingat' least 15% Y this 'venton ar Said under thi-Bftish t EL f SOZ by Weight' "The ethyl 'siliaie hydlplysis is arleid" mark S tori ard have'the followiln ifcgesrties'l a e" out by theiwater present inthe silicasol. IThisallowsol v f y ,i i i p p i si; the rireparationy of hydrolysed ethyl silicatesolutionshav; 40 img a greater silica content than has hitherto. been possible'. ,i Slhcasol' No' 1 Hamid Gamm Emblem, Melbourne, andDesiandJqsepii-'f yCloherty, Chellaston,y England, assignors 'to" Rolls 'l'lie'hydrolysisI may be carried fout-in the presence of a 2i;-

Isl?ninifr;"`"';`' gewent by 'Weight'. "mutual solvent, or by emulsifying the ethyl silicatewithu Avgrgg'-ftglfagfe: 1,566 Av the acidied'stable silica sol. a `As ethylk 'licate and water are immiscible the hydroly- Sold as. Syn?? sisL is best carried out in a mutual lsolvent for ethylsili- Silica SOL NQ 2: t f

cate'and Athewater present inthe stable-silica'sol@ A"'Ex- 1 esjc-acntem: ,30 percent by w'ght` t `a'r'ipl'es offsuitable mutual solventsv are acetone, ethyl PH: ;;LL LL i10 0 a alcoholandisopropanolalcohol. vOffthese solvents, ethyl )1 Averge'particle diameten 250 A i alcohol andrisopropanol lare preferred. w 1v Sold as fsyton 2X ,i The .degree-'of acidication of the stable silica sol con-` 50 if i, o. i i, ,vg Y `trsl-the rate O15-hydrolysis 0f the ethyl silicate',` and also v al y:A suitable ethylisilicate is thatsold under the British v -llefimeffgelatiml O fth resulting hydrolysedfeffhylsilregistered trademark Silester as Silester 0. Qff'S'Ol'llfionlIf thefreactionis to be Carried O ut in the; SilesteriO is an ethyl silicatenprepared `by the reaction Presence 0f a mutual Solvellt: e- 8f ethyl alcohol '0f SO" of-Lsilicon tetrachloride amd64 over proof ethyl-alcohol. prop'anol alcohol, for ethyl' silicate' and the stable silica 55 gIt .hasy aiypial analysis as follows,v au percentages sol, y:it is essential that the-stablesilica s ol should be -frbeing byw'eight; i f ac'idie'd before adding thefsolvengto prevent uncontrol l j j :lable'f 'ge lation of the,y sol. In order to dilute the vs 'ol asjj Specific gravity`l.,05 to 1.07 at 20 C.

little 'asf possible,it isy desirable to acidify the sol"b y adding Aidityas percent HCl0.l% maximum. l -v ii'centrate'dacid. If theacid tobe used is hydrochloricvv 60 Percent egrcess ethyl alcohol-4% maximum,

acid,v one suitableacid is a commercial conceritratedliyf-v rqfSili'ca content as percent 'SiOZl-AQ-l d roehloric acid solution, having a specific gravity'of not f f z -les's'than l-.lZcorrespondirig to a normality of y7.3. A Suitable refractory materials-to use with bonding 4preferred hydrochloric acid solution lis one having a `liquids according to this invention to form a mould are specific gravitybetiveen l.'l'4 and 1.18, corresponding to 65 silia', 'the` aluminumsilicates such as sillimanite, calcined a 'normality of vbetween 8.8 and 1 ,1; 8.r Sulphuric acidf y,fkaolin,:iiireclay grog` togetherjwith zircon and zirconia.

solutions of thesaine normality rneare also suitable. Iiithe Viriaterials the lime, mag'nesia and 'alkali' content vPrefer'ablythe normality of thejacidied'silica sol'isin the shouldnot exceed 4'perc'ent byweight rgejOQS-LZ toobtain a desired time of gelation. The v It 'will' be realised that other refractory materials may "iigu'res'iinlthis range of-'normalityare vobtained:by'facldiri'gf70 lbe used in laddition tothose listed provided that, they 4thejacid to the silica sol andtitratinglvvith standard 'alkali" have'not'an;excessive alkalicontent f using' niethyl'ora'nge as an indicator.V v Thefollowing 'are examples given' by vvay Akof'l'illustiaetion Aof ways of preparing bonding lig/"ids accordinghto v l EXAMPLE 2 2 cc. of commercial concentrated hydrochloric yacid solution were added to 26 cc. of Syton 12X(silca sol No. 2). 35 ec. of 64 O. P. ethyl'alcohol'were next added followed by 84 cc. of ethyl silicate (Silester O). 30 minutes later 47 cc. of ethyl silicate (SilesterO) were added, the solution being ready for use at this stage. It is essential to add the components in the order'given.

EXAMPLE 3 50 cc. of commercial concentrated hydrochloric acid solution were added to 1300 cc. of Syton 2X (silica soll No. 2). 3500 cc. of 64 O. P. ethyl alcohol were next added followed by 8400 cc. `of ethyl silicate A(Silester O). One hourV later 6700 cc. of ethyl silicate (Silester O) were added, the solution 'being ready foruse Vat this stage. It is essential to add the components in the order given and approximately at the times-scheduled.

The mould investment slurry using this liquid binder may be prepared in the following manner:

2 cwts. of a refractory filler containing 'approximately equal parts by weight of Zircon sand and calcined-kaolin were added to all the bonding liquid prepared in accordance with Example No. 3 half an hour after the preparation of that liquid was completed. The refractoryvller had the following chemical analysis and particle sizedstribution:

A. Chemical analysis The mould is formed by vibration of the invested pattern to consolidate the refractory in the slurry.

EXAMPLE 4 To 9,000 cc. of Syton 2X (silica sol No. 2) were added 600 cc. of concentrated hydrochloric acid, followed by 15,000 cc. of 64 O. P. ethyl alcohol. 60,000 cc. of ethyl silicate (Silester O) were added to the mixture, which was stirred for l hour before use. It is essential-to add the reagents in the order given.

An investment slurry was prepared by mixing 14 litres of the above solution with 112 lbs.v of the refractory .filler used in Example 3.

4 This gives a rather stiff slurry. A more fluid slurry may be prepared by using 15 litres of the solution.

After vibration of the invested patterns the resulting moulds are heated at a temperature between 35 C. and 40 C.,fgor 4 days, to gel the bonding liquid. The mould is then heated at a temperature between 95 C. and 100 C. for at least 24 hours, to remove the wax pattern, then gradually heated to a temperature of approximately 1000 C. over a period of 8 hours, being held at approximately 1,000 C. for at least two hours, and preferably for not less than 10 hours, prior to the casting operation.

EXAMPLE 5 ToV 4,400 cc. of Syton 2X (silica sol No. 2) were added 400 cc. of concentrated hydrochloric acid, followed by 7,500 cc. of 64 O. P. ethyl Ialcohol. 30,000 cc.

of ethyl silicate (Silester O) were added to the mixture,

which was stirred for three hours before use. It is essential to add the reagents in the order given.

An investment slurry was prepared by mixing 20.5

litres of the above solution with 112 lbs. of the refractory ller usedin Example 3. Thisrgives a tluid slurry,

^ 95' C. and 100 C. for at least 24 hours to remove the 11,000 cc. of 64 O. P. ethyl alcohol.

wax pattern. The moulds are then gradually heated to a temperature of approximately 1,000" C. over a period of 8 hours, being held at approximately 1,000 C. for at least two hours, and preferably for not less than ten hours, prior to the casting operation.

EXAMPLE 6 To 6,750 cc. of Syton 2X (silica sol No. 2) were added 300 cc. of concentrated hydrochloric acid, followed by 45,000 cc. of ethyl silicate (Silester O) were added to the above mixture, which was stirred for three hours before use. It is essential to add the reagents in the order given.

An investment slurry was prepared by mixing 21 litres of Vthe above solution with 112 lbs. of ireclay grog,

having an alumina percentage of 44, and aparticle size distribution as given below.

B. S. S. 410, 1943, sieve No.: Percent retained 16 2.1 30 23.3 52 19.1 72 10.0 7.4 9.3 200 6.4 Pass 200 22.2

After vibration of the invested patterns, the resulting moulds Vare treated as described in Example 4.

EXAMPLE 7 To 30 cc. of Syton 2X were added 2 cc. of a sulphuric acid solution prepared by the dilution with water of -concentrated sulphuric acid of specific gravity 1.84, so

that 15 cc.` of the concentrated sulphuric acid were con-V ltained in 50 cc. of the diluted acid solution. This diluted Madded, especially during vthe additionof the` sulphuric `acid solution and the ethyl silicate.

The hydrolysed ethyl silicate solution is miscible with V[with thelatter value.

f bine stationary blades of gas turbine engines.

rcation Serial No. 444,363,` iiled July 19, 1954, abandoned.

acetone, benzene and ethyl silicate. and may be gelled by an aqueous solution of ammonium carbonate. mls. of a solution of 8 gms. of' ammonium carbonate, B.y P.

grade, in 100' mls. of water were found to gel 50 cc. 'of the above hydrolysed ethyl silicate'solution in aboutk 3 minutes EXAMPLE 8 y To cc. of Syton 2X were added 2 cc. ofconcentrated ,l

hydrochloric acid solution, followed 'by 125 cc. of'ethyl silicate (Silester O). The mixture was'stirredvigorously during the addition of the reagents and while the hydrolysisreaction proceeded... When the temperature of the mixture began to fall a further 150 cc. of ethyl'silicate f (Silester O) werev added. The solution is'ready for vuse .when cold.

In the .above Examples 1 to 6 and 8 the concentrated tionr we have :been able to construct investment moulds of considerably increased strength to those known tous xhitherto.

" production of the long slender cores used, in the production of certain hollow castings, for example hollow tur- This advantage has permitted inter alia the This application is a continuation-impart of our applinow What we claim is:

prepared by carrying out the hydrolysis of yethyl silicate with a stable silica sol to which has been added an acid vselected from the group which includes hydrochloric and sulphuric acids toproducea'normality of the acidiiiedv i silica sol in the range.'0.2`5. to 1.2.

2. A bonding liquid -asy `claimed in clailnfl in which` the hydrolysis of ethyl silicate is carried out in a mutual solvent for ethyl silicate vand water present inthe stable v silica sol. Y; i Y f 3. A vbonding liquid as claimed in claim2 in which o the mutualsolventis 'chosen ,from the group acetone,

` ethyl alcohol and isopropanol.

4. Afbondingv liquid as maimed in claim 1'., ia which" f the added acid is a concentrated hydrochloric acid soluv tion having a specicngravity of not lless than1 1.12.

5. A bonding liquid as claimed in claim 3 in which the 'added acid is hydrochloric having a specic gravity of V'from 1.14 to 1.18.k H

6. A bonding liquid claimed in claim 1 in which' fthe added acid is a high concentration of sulphurieacidv having a normality not less than 7.3. ,f

' v7. A bonding liquid as claimed in claim 1 v8. Av bondingliquid as claimedin claim linwhich the I stable silica sol contains at vleast l15 percentl of SiO2 by r1. A 'bonding liquid for bonding refractory materials used for moulds and cores in precision casting which is weight.

which theacid has been added.

Y References Cited in the of this patent UNITED STATES PATENTS v722,425 Great Britain 1an. 26, 1955 OTHER REFERNCES ller: The Colloid Chemistry of Silicat silicates, pub- "lihed by 00mg!! Univ- Prw (.1955), Page845. 4. 4,9, 55

r, in whieh the] .added acid is sulphuric acid having a normality between 8.8 and v11,8. v i

bonding liquid as claimed injclaim 1 in which the y lethyl silicate 'has been emulsed by thesilicarol to 

1. A BONDING LIQUID FOR BONDING REFRACTORY MATERIALS USED FOR MOULDS AND CORES IN PRECISION CASTING WHICH IS PREPARED BY CARRYING OUT THE HYDROLYSIS OF ETHYL SILICATE WITH A STABLE SILICA SOL TO WHICH HAS BEEN ADDED AN ACID SELECTED FROM THE GROUP WHICH INCLUDES HYDROCHLORIC AND SULPHURIC ACIDS TO PRODUCE A NORMALITY OF THE ACIDIFIED SILICA SOL IN THE RANGE 0.25 TO 1.2. 